Mike Burton

Spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas

Lava fountains are spectacular continuous gas jets, propelling lava fragments to heights of several hundred metres, which occasionally occur during eruptions of low-viscosity magmas. Whether they are generated by the effervescent disruption of fast-rising bubbly melt or by the separate ascent of a bubble foam layer accumulated at depth still remains a matter of debate. No field measurement has yet allowed firm discrimination between these two models. A key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase. This composition should differ markedly depending on whether the magma degassing occurs before or during eruption. Here we report the analysis of magmatic gas during a powerful (250–600 m high) lava fountain, measured with Fourier transform infrared spectroscopy on Mount Etna, Sicily. The abundances of volcanic gas species, determined from absorption spectra of lava radiation, reveal a fountain gas having higher CO2/S and S/Cl ratios than other etnean emissions, and which cannot derive from syn-eruptive bulk degassing of Etna basalt. Instead, its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1.5 km depth below the erupting crater.

Chronology and complex volcanic processes during the 2002--2003 flank eruption at Stromboli volcano (Italy) reconstructed from direct observations and surveys with a handheld thermal camera

[1] Effusive activity at Stromboli is uncommon, and the 2002–2003 flank eruption gave us the opportunity to observe and analyze a number of complex volcanic processes. In particular, the use of a handheld thermal camera during the eruption allowed us to monitor the volcano even in difficult weather and operating conditions. Regular helicopter-borne surveys with the thermal camera throughout the eruption have significantly improved (1) mapping of active lava flows; (2) detection of new cracks, landslide scars, and obstructions forming within and on the flanks of active craters; (3) observation of active lava flow field features, such as location of new vents, tube systems, tumuli, and hornitos; (4) identification of active vent migration along the Sciara del Fuoco; (5) monitoring of crater’s inner morphology and maximum temperature, revealing magma level changes within the feeding conduit; and (6) detection of lava flow field endogenous growth. Additionally, a new system developed by A. J. L. Harris and others has been applied to our thermal data, allowing daily calculation of effusion rate. These observations give us new insights on the mechanisms controlling the volcanic system.

Remote sensing of CO2 and H2O emission rates from Masaya volcano, Nicaragua

Although CO 2 and H 2 O account for more than 90 mol% of volcanic gases, the rates at which these gases are emitted from volcanoes are difficult to determine because of their high atmospheric background levels. We report the first precise field measurements of volcanic CO 2 , and H 2 O, in addition to HCl, HF, and SO 2 , in the plume of Masaya volcano, Nicaragua, a basaltic volcano with a record of Plinian activity. The molar ratios for CO 2 : SO 2 (2.3–2.5) and H 2 O: SO 2 (66–69) observed in February–March 1998 and March 1999 show no significant variation over the 12 month period. The molar composition of the gas is similar to other basaltic arc volcanoes in Central America. Emission rates of SO 2 from the summit crater, determined by correlation spectroscopy, averaged 21 kg s −1 during the study periods, indicating CO 2 , H 2 O, HCl, and HF emission rates of 32–36, 380–420, 7.0–7.8, and 0.86–0.95 kg s −1 , respectively. At these rates it takes only a few years to emit the equivalent volatiles associated with Masaya9s prehistoric Plinian eruptions.

Remote measurements of volcanic gas compositions by solar occultation spectroscopy

Volcanic gases have important effects on the atmosphere and climate, and are important indicators of subsurface magmatic processes,, but they are difficult to measure. In situ sampling on volcanoes can provide detailed information but is often impractical or hazardous. It is safer to apply remote techniques, for example correlation spectroscopy, which is now widely used to estimate emission rates of sulphur dioxide; but making remote measurements of other gas species has proved more difficult. Developments in Fourier-transform infrared spectroscopy, however, have shown promise. Here we report Fourier-transform infrared observations of volcanic plume compositions that we obtained by solar occultation at Mount Etna in 1997. We foundmolar ratios of SO2:HCl and SO2:HF to be ∼4.0 and 10, corresponding to emission rates of HCl and HF of about 8.6 and 2.2 kg s−1, respectively, confirming Mount Etna as the largest known sustained point source of these gases. Solar occultation spectroscopy has advantages over other methods as it enables measurement of plume compositions several kilometres downwind, without requiring hot rocks or lamp sources. The regular and frequent observation of volcanic gases provides a valuabletoolfor volcano surveillance, and data from plumes at different distances downwind of a volcanos summit may help us to understand the atmospheric chemistry involved in plume dispersal.

Effusive to explosive transition during the 2003 eruption of Stromboli volcano

The persistent explosive activity of Stromboli volcano (Italy) ceased in December 2002 and correlated with the onset of a seven-month-long effusive eruption on the volcano flank from new vents that opened just below the summit craters. We intensively monitored this effusive event, collecting and interpreting, in real time, an extensive multiparametric geophysical data set. The resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical Strombolian activity. We present a direct link between gas flux, magma volume flux, and seismicity, supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity. This insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity.

Continuous soil radon monitoring during the July 2006 Etna eruption

[1] Continuous soil radon monitoring was carried out near the Southeast Crater (SEC) of Mt. Etna during the 10-day July 2006 Strombolian-effusive eruption. This signal was compared with simultaneously acquired volcanic tremor and thermal radiance data. The onset of explosive activity and a lava fountaining episode were preceded by some hours with increases in radon soil emission by 4–5 orders of magnitude, which we interpret as precursors. Minor changes in eruptive behavior did not produce significant variations in the monitored parameters. The remarkably high radon concentrations we observed are unprecedented in the literature. We interpret peaks in radon activity as due primarily to microfracturing of uranium-bearing rock. These observations suggest that radon measurements in the summit area of Etna are strongly controlled by the state of stress within the volcano and demonstrate the usefulness of radon data acquisition before and during eruptions. Citation: Neri, M., B. Behncke, M. Burton, G. Galli, S. Giammanco, E. Pecora, E. Privitera, and D. Reitano (2006), Continuous soil radon monitoring during the July 2006 Etna eruption, Geophys. Res. Lett., 33, L24316, doi:10.1029/ 2006GL028394.

Changes in gas composition prior to a minor explosive eruption at Masaya volcano, Nicaragua

Abstract A small explosive eruption at Masaya volcano on 23 April 2001, in which a number of people were injured, was preceded by a distinct change in plume gas compositions. Open-path Fourier transform infrared spectroscopy (FTS) measurements show that the SO 2 /HCl molar ratio increased from 1.8 to 4.6 between April 2000 and April/May 2001. The SO 2 flux decreased from 11 to 4 kg s −1 over this period. We interpret these changes to be the result of scrubbing of water-soluble magmatic gases by a rejuvenated hydrothermal system. A sequence of M 5 earthquakes with epicentres about 7 km from the volcano occurred in July 2000. These may have altered the fracture permeability close to the magmatic conduit, and caused increased magmatic–hydrothermal interaction, leading eventually to the phreatic explosion in 2001. Continuous FTS measurements at suitable volcanoes could provide useful information in support of eruption prediction and forecasting.

High spatial resolution radon measurements reveal hidden active faults on Mt. Etna

Radon emissions are frequently monitored in volcanically and tectonically active areas in order to reveal changes in soil degassing, as radon acts a tracer for the more abundant CO2 degassing commonly observed in such areas. Between July 2002 and May 2003 a series of discrete measurements of radon concentrations in soil were made with high spatial resolution (similar to5 - 100 m) in the Santa Venerina area on Mt. Etna. These measurements revealed well-defined linear anomalies that we interpret as being caused by active faults whose higher porosity than surrounding soils allows an increased CO2 flux, carrying radon from beneath. These faults were not visible at the surface and were therefore revealed at high spatial resolution by our radon survey. Our hypothesis that the positive anomalies are attributable to active faults was strengthened by the observation of concentrated damage along this geometry during the earthquakes that struck this area in late October 2003.

The relationship between degassing and ground deformation at Soufriere Hills Volcano, Montserrat

We examine the correlations between SO2 emission rate, seismicity and ground deformation in the month prior to the 25 June 1997 dome collapse of the Soufriere Hills Volcano, Montserrat. During this period, the volcano exhibited a pattern of cyclic inflation and deflation with an 8‐14 h period. We find that SO 2 emission rates, measured by COSPEC, correlate with the amplitude of these tilt cycles, and that higher rates of SO 2 emission were associated with stronger ground deformation and enhanced hybrid seismicity. Within tilt cycles, degassing peaks coincide with maximum deformation gradients. Increases in the amount of gas in the magma conduit feeding the dome, probably due to increases in volatile content of ascending magma volume can account for the observed increases in tilt amplitude, hybrid seismicity and SO2 emission rate. q 2000 Elsevier Science B.V. All rights reserved.

Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow

Driven to collapse Volcanic eruptions occur frequently, but only rarely are they large enough to cause the top of the mountain to collapse and form a caldera. Gudmundsson et al. used a variety of geophysical tools to monitor the caldera formation that accompanied the 2014 Bárdarbunga volcanic eruption in Iceland. The volcanic edifice became unstable as magma from beneath Bárdarbunga spilled out into the nearby Holuhraun lava field. The timing of the gradual collapse revealed that it is the eruption that drives caldera formation and not the other way around. Science, this issue p. 262 Magma flow from under the Bárdarbunga volcano drove caldera collapse during the 2014 eruption. INTRODUCTION The Bárdarbunga caldera volcano in central Iceland collapsed from August 2014 to February 2015 during the largest eruption in Europe since 1784. An ice-filled subsidence bowl, 110 square kilometers (km2) in area and up to 65 meters (m) deep developed, while magma drained laterally for 48 km along a subterranean path and erupted as a major lava flow northeast of the volcano. Our data provide unprecedented insight into the workings of a collapsing caldera. RATIONALE Collapses of caldera volcanoes are, fortunately, not very frequent, because they are often associated with very large volcanic eruptions. On the other hand, the rarity of caldera collapses limits insight into this major geological hazard. Since the formation of Katmai caldera in 1912, during the 20th century’s largest eruption, only five caldera collapses are known to have occurred before that at Bárdarbunga. We used aircraft-based altimetry, satellite photogrammetry, radar interferometry, ground-based GPS, evolution of seismicity, radio-echo soundings of ice thickness, ice flow modeling, and geobarometry to describe and analyze the evolving subsidence geometry, its underlying cause, the amount of magma erupted, the geometry of the subsurface caldera ring faults, and the moment tensor solutions of the collapse-related earthquakes. RESULTS After initial lateral withdrawal of magma for some days though a magma-filled fracture propagating through Earth’s upper crust, preexisting ring faults under the volcano were reactivated over the period 20 to 24 August, marking the onset of collapse. On 31 August, the eruption started, and it terminated when the collapse stopped, having produced 1.5 km of basaltic lava. The subsidence of the caldera declined with time in a near-exponential manner, in phase with the lava flow rate. The volume of the subsidence bowl was about 1.8 km3. Using radio-echo soundings, we find that the subglacial bedrock surface after the collapse is down-sagged, with no indications of steep fault escarpments. Using geobarometry, we determined the depth of magma reservoir to be ~12 km, and modeling of geodetic observations gives a similar result. High-precision earthquake locations and moment tensor analysis of the remarkable magnitude M5 earthquake series are consistent with steeply dipping ring faults. Statistical analysis of seismicity reveals communication over tens of kilometers between the caldera and the dike. CONCLUSION We conclude that interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual near-exponential decline of both the collapse rate and the intensity of the 180-day-long eruption. By combining our various data sets, we show that the onset of collapse was caused by outflow of magma from underneath the caldera when 12 to 20% of the total magma intruded and erupted had flowed from the magma reservoir. However, the continued subsidence was driven by a feedback between the pressure of the piston-like block overlying the reservoir and the 48-km-long magma outflow path. Our data provide better constraints on caldera mechanisms than previously available, demonstrating what caused the onset and how both the roof overburden and the flow path properties regulate the collapse. The Bárdarbunga caldera and the lateral magma flow path to the Holuhraun eruption site. (A) Aerial view of the ice-filled Bárdarbunga caldera on 24 October 2014, view from the north. (B) The effusive eruption in Holuhraun, about 40 km to the northeast of the caldera